Transmission electron microscopy (EM) is used as an adjunct procedure in the diagnosis of a wide range of neoplastic and non neoplastic diseases and can be extremely useful in well chosen diagnostic dilemmas. The main objectives of the diagnostic EM service are: (1) to provide high quality EM diagnostic services to NCI- and NIH-supported clinical diagnostic and treatment protocols (2) to help elucidate the pathogenesis of disease processes studied in these protocols (3) to teach pathology residents and fellows the application of EM in the diagnosis of human diseases and (4) to provide electron microscopic expertise to the NIH scientific community. The last year's accomplishments are summarized below: (1) A total of 100 patient tissues were processed and diagnosed by EM. The service is regularly inspected and certified by CAP. (2) Research specimens with multiple samples per specimen were processed and evaluated, resulting in 7 publications. (3) Invitation by the Society of Ultrastructural Pathology to lecture in the society's companion meeting on "the routine use of electron microscopy and other adjunct diagnostic techniques in pediatric neoplasms" (US-CAP meeting, Chicago, Feb. 24, 2002)